Endocrine factors contributing to the regulation of folliculogenesis (selection of the dominant follicle) during the primate ovarian cycle were examined in two non-human primate models, the rhesus monkey, and the cynomolgus monkey. Circulating patterens of gonadotropins and ovarian steroids (estradiol and progesterone) were monitored by radioimmunoassay before and after follicle cautery, luteectomy and during the menstrual cycle in monkeys. In addition to examining follicle growth during the nonfertile menstrual cycle, the resumption of follicle growth was studied during the puerperium. Ovary conceptus interrelationships, as well as the cessation of follicle growth in pregnancy were studied during the fertile menstrual cycle. Salient findings include: 1) usefulness of the cynomolgus monkey as alternative non-human primate model, 2) asymmetrical function of the two ovaries during the menstrual cycle, 3) evidence that the dominant follicle is selected during the first of the menstrual cycle, 4) onset of asymmetrical ovarian function prior to the onset of ovulatory cycles in juvenile monkeys, and 5) the enhanced biological activity of LH associated with the onset of the first ovulatory cycles and at mid-cycle in adult ovulatory monkeys.